Chemical nickel plating on nonmetallic materials



Sept. 28, 1954 G, GUTZEH' ETAL 2,690,403

CHEMICAL NICKEL PLATING ON NONMETALLIC MATERIALS Filed July 24, 1955 w m IniaT/on Time, Minutes INVENToRs .Gregoire Gufzei BY Wil/iam .I Cre/1an Abraham Krieg MMM/WAM,

Patented Sept. 28, 1954 UNITED STATES PATENT OFFICE CHEMICAL NICKEL PLATING ON NON- METALLIC MATERIALS Application July 24, 1953, Serial No. 370,142

(Cl.V 117-47) 6 Claims. i

The present invention relates to processes of chemical nickel plating of non-conductive and non-catalytic solid materials and to methods of preparing the surfaces of such materials so that a homogeneous and adherent lm I nickel may be chemically deposited thereon. This application is a division of the copending application of Gregoire Gutzeit, William J. Crehan and Abraham Krieg, Serial No. 230,352, filed June 7, 1951.

In the copending application of Gregoire Gutzeit and Abraham Krieg, Serial No. 194,656, led November 8, 1950, now Patent No. 2,658,841, granted November 10, 1953, there is disclosed a process of chemically plating with nickel, metals and other catalytic materials, by contacting the materials with an acid bath containing nickel ions and hypophosphite ions and a butler. This process is carried on under certain optimum conditions, which are as follows:

The ratio between nickel ions and hypophosphite ions in the bath, expressed in molar concentrations, is within the range from 0.25 to 0.60; the absolute concentration of hypophosphite ions in the bath expressed in mole/liter, is within the range from 0.15 to 0.35; the absolute concentration of the buffer in the bath is approximately equivalent to two carboxyl groups for every nickel ion that can be deposited, for instance, in the case of sodium acetate, 0.120 mole/liter of acetate ion; the initial pI-I of the bath is within the approximate range from 4.5 to 5.6; the temperature of the bath is slightly below the boiling point thereof, about 93 centigrade; and the ratio between the volume of the bath, expressed in cubic centimetres (cm) and the surface area of the material that is to be plated expressed in square centimetres (cm2), (V/A), is not greater than 10. The buffers mentioned in that application and employed in the tests therein referred to are soluble salts of simple short chain aliphatic monocarboxylic acids with an ionization constant pKa, higher than 4.7; such as, acetic acid, butyric acid, propionic acid, etc.

In the copending application `of Gregoire Gutzeit and Ernest J. Rairez, Serial No. 204,424, led January 4, 1951, now Patent No. 2,658,842, granted November 10, 1953, there is disclosed a process of chemically plating with nickel, metals and other catalytic materials, by contacting the materials with an acid bath containing nickel ions and hypophosphite ions and an exaltant. This process is carried on under certain optimum conditions, which are as follows:

The ratio between nickel ions and hypophosphite ions in the bath, expressed in molar concentrations, is within the range from 0.25 to 1.60; the absolute concentration of hypophosphite ions in the bath, expressed in moles/liter, is within the range 0.15 to 1.20; the absolute concentration of the exaltant in the bath is approximately equivalent to two carboxyl groups for every nickel ion that can be deposited, for instance, in the case of sodium succinate, at least 0.05 mole/liter of succinate ion; the initial pH ofthe bath is within the approximate range 4.3 to 6.8; the temperature of the bath is slightly below the boiling point thereof, about 99 centigrade; and the ratio between the volume of the bath, expressed in cm, and the surface area of the material that is to be plated, expressed in om?, (V/A), is not greater than 10. The exaltants mentioned in this last mentioned application and employed in the tests therein referred to are soluble salts of simple short chain aliphatic dicarboxylic acids with an ionization constant pK2 higher than 5.4; such as malonic acid, succinic acid, glutaric acid, etc.

In the applicationsv referred to, it was pointed out that the catalytic materials thaty could be plated; with nickel employing the bathsv and processes set forth were materials which cause the plating reaction:

zur? oar Ni +111] For instance, using nickel chloride to provide the nickel ion and sodium hypophosphite to provide the hypophosphite ion;

mandarci) Ni 2301+ Hi In. other words, materials that catalyze the oxidation of the hypop-hosphite ion to the phosphite ion, while reducing water to atomic hydrogen, and, at the same time, promoting the formation of molecular hydrogen comprises catalytic materials. This reaction can be ascertained by observing and measuring the volume of hydrogen gas evolved in an aqueous solution of a soluble hypophosphite upon addition of the catalytic material, preferably at. the highest possible temperature below the boiling point of the solution. The following elements are catalytic: C11, Ag, Au, Be, B, Ge, Al, Tl, Si, C, V, Mo, W, Cr, Se.. Te, Ti, Fe, Co, Ni, Pd and Pt; and the following elements are definitely noncatalytic: Bi, Cd, Sn, Pb and Mn.

Nonconductive and noncatalytic materials, such as plastics, hard rubber, wood, ceramics, etc., do not cause the plating reactions (l) and (2); and thus cannot be plated with nickel directly in accordance with the processes set forth in the applications mentioned.

Accordingly, it is the general object of the present invention to provide a process of chemical plating with nickel the surfaces of non-conductive and non-catalytic materials, such as plastics, hard rubber, wood, ceramics, etc.

Another object of the invention is to provide a method of preparing the surface of a non-conductive and non-catalytic material of the character mentioned so that it may be chemically plated with nickel.

A further object of the invention is to provide a method of preparing the surface of a nonconductive and non-catalytic material so that it may be chemically plated with nickel employing substantially the improved processes described in the applications mentioned above.

These and other objects and advantages of the present invention will be understood from the foregoing and the following description taken with the accompanying drawings, in which:

Figure 1 shows the variations in the initiation time interval of nickel plating upon prepared noncatalytic samples with variations in ratios of nickel ions to hypophosphite ions in the chemical nickel plating baths containing sodium salts; and

Fig. 2 shows the variations in the initiation time interval of nickel plating upon prepared non-catalytic samples with variations in ratios of nickel ions to hypophosphite ions in chemical nickel plating baths containing calcium salts.

In accordance with the present invention, in order to obtain nickel chemical plating of nonconductive and non-catalytic materials, such as plastics, hard rubber, wood, ceramics, etc., it is necessary first to prepare or condition the surface of the material prior to contacting it with the chemical nickel plating bath. More particularly, the surface of the material is modified so as to form thereon firmly anchored growth nuclei. It is not necessary to achieve a complete coverage of the surface of the material with the growth nuclei, as the nickel plating will spread for a certain distance from each growth nucleus in the two dimensions along the surface of the material as it builds up in the third dimension upon the growth nucleus, thereby obtaining ultimately a complete and homogeneous coating of nickel upon the surface of the material. of the material is modified to eliminate polarization of the areas between the growth nuclei by effecting the presentation in these areas of a fresh surface.

In one form of the method, the surface of a non-conductive and noncatalytic material of the character referred to may be prepared for chemical nickel plating by freshening and contaminating it with traces of a catalyst in such a manner that the catalytic particles are securely anchored in place upon the freshened surface. By simply dusting the surface with finely divided carbon particles, a coating is provided so that nonconductive and noncatalytic material of the character mentioned is prepared for chemical nickel plating. However, in order to obtain good aclhesion of the subsequently deposited nickel to the material, the catalyst must be firmly anchored to the surface of the material and the surface of the material must be fresh; whereby as many Also, the surface growth nuclei as possible are securely anchored to the surface of the material, and the catalytic areas on the surface of the material are not polarized. These conditions may ordinarily be obtained by removing the surface skin of the material as the carbon particles are embedded in the freshly presented surface of the material.

In another form of the process where an artificial or compounded non-conductive and noncatalytic material is produced by forming, molding or casting, the carbon particles may be mixed with the basic material prior to forming, etc. As only the amount of carbon particles present at the surface of the formed material isy useful, enough carbon particles should be added to the basic material initially to provide adequate growth nuclei at the boundary or surface of the formed material. The formed material is subsequently prepared by sanding, blasting, brushing, tumbling, chemical etching, etc., to expose a fresh surface thereon prior to being subjected to the nickel plating bath. For instance, by compounding a thermosetting plastic molding powder, (e. g. Bakelite) with 15% carbon particles, by weight, molding the compound under heat and pressure, then subjecting the surface of the article thus formed to a fine abrading action by liquid honing in order to prepare the surface thereof, and, finally, chemically nickel plating the prepared surface of the article, an eX- cellent, adherent and continuous nickel coating may be obtained.

A further form of the process is generally applicable to most non-conductive and non-catalytic materials, and comprises employing mechanical pressure to incorporate the carbon particles into the surface of the material while simultaneously freshening the surface of the material. This can be achieved by Such operations as wet or dry blasting, brushing, tumbling, sanding, wire wheel brushing, and the like, using a mixture of abrasive and carbon particles. For instance, liquid honing with Vapor Blast equipment using Novaculite 325 or 1250 mesh abrasive mixed with 30% carbon particles has been found to be excellent in the preparation of the surfaces of materials for chemical nickel plating. Also dry blasting with 325 mesh emery powder and 30% carbon particles has been found to be useful in the preparation of the surfaces of the material; and the same is true with activated sanded surfaces obtained by powering the sand belt with carbon particles.

In the preparation of the surface of the noncond'uctive and noncatalytic material, it is usually advisable just preceding the transfer of the material to the chemical nickel plating bath to subject the surface thereof to a standard cleaning operation, using techniques familiar to the metal working trade which will not deactivate the surface, such for instance as spray washing with a detergent, vapor degreasing, etc. This final standard cleaning step is unnecessary and may be omitted when the surface of the material is prepared or activated by certain of the steps described above, including liquid honing and steam blasting, since these steps will usually effect the necessary standard cleaning or degreasing simultaneously with the activation or preparation of the surface of the material.

In accordance with the process of the present invention after the surface of the non-conductive and non-catalytic material has been activated or prepared in accordance with the method described above, the material is transferred to fafeoogios the chemical nickel 'plating bath in .order that .the plating of the nickel fon lthesurface thereof is first initiated and then continued. The chem- .ical .nickel plating bath employed may be that disclosed in either `of the .previously noted applications; however, in employing either of 'these maths, itis advantageous to :use a bath Acomposition having a nickel ion to hypophosphite ion ratio toward the lower extremity of the range set forth, as it has been discovered that such lower Ni++/(H2PO2)" ratio baths initiate the nickel plating upon the previously activated or prepared surface of the non-conductive and noncatalytic material in an appreciably shorter time interval than do the higher Ni++/(H2PO2) ratio baths.

In this connection, it will be apparent that once nickel plating on the surface of the material has been initiated, i. e., proceeded -to a 'point where the surface thereof is covered with `a continuous film of nickel, even a monomolecular layer, the conditions with respect to continued nickel plating become identical to those prevailing in the plating of catalytic materials las disclosed in the said applications previously mentioned. In other words, a different state exists onlyat the Vbeginning of the chemical nickel plating reaction inthe case vof a non-conductive and non-.catalytic material having a previously 'prepared or activated surface. Moreover, it has .been discovered that the best conditions for obtaining a `first uniform and continuous flash `of .nickel plating upon the previously prepared vor activated surface of the non-conductive and non-catalytic material are somewhat different from the best-conditions for obtaining continued nickel plating of the surface after the flash layer of metallic nickel has been obtained. Thus, .it will be understood that after the flash coating of nickel upon the surface of the material has been obtained, the material may be trans- In other words, the more the chemical nickel plating bath tends 'toward chemical non-selective random reduction of nickel ions, as 4shown .by thermal decomposition tests or by the early appearance of black precipitate during plating, the faster the chemical nickel plating bath will initiate. However, the presence of black precipitate ordinarily causes a rough deposit of metallic nickel upon the material undergoing the plating operation, as well as a rapid depletion of nickel ions in the bath by autocatalytic decomposition. Therefore, it is `necessary to obtain in the chemical nickel plating bath that is employed for initiating the flash deposit of the nickel upon the material, a compromise between stability and the time interval lag to achieve the initiation mentioned.

Considering first a bath of the lgeneral character of that disclosed in the previously mentioned application of G-utzeit and Krieg, when alkali compounds are used as reagents, the buffer being a salt of a short chain aliphatic monocarboxylic acid, such as sodium acetate, the optimum concentration of the hypophosphite ions derived from alkali hypophosphite is again between 0.15 and 0.35 mole/liter. The initiation time is practically a straight line function of the ratiol of nickel ions to hypophosphite ions, but relatively large amounts of black precipitate are formed at the lowest Ni++/(I-lzPO2) ratios, although ythe quality of the plating is still good within the optimum range of Ni++/(l-I2PO2) of 0.215 to 0.60. The following tabulation summarizes .tests run in cc. of :chemical nickel plating bath at a V/A ratio of 2.5 on activated general purpose Bakelite samples; the absolute concentration of hypophosphite ions derived from sodium hypophosphite was 0.224 mole/liter; the buffer was sodium acetate and its concentration in acetate ions` was 0.120 mole/- liter; and the initial pI-I was adjusted to 4.85:

lferred to :one `of the previously mentioned baths l'xaving a higher Nitt/(HzPOD ratio, in order to continue the plating of the nickel upon the flash coating of nickel deposited upon the surface of .the material, although this transfer is 4not 'essential and is suggested only when it is :desired to obtain a rather thick nickel coating vin a minimum time interval.

Accordingly, it will be understood that the followingconsiderations pertain to the composition of ychemical nickel plating rbaths that are provided specifically for the purpose of initiating the nickel plating upon the previously prepared and activated surface of a non-conductive vand non-catalytic material, it being desirable to initiate the .ash coating of nickel in `the yminimum time, time intervals of ten minutes, or less, being preferable.

In a general way, it can be stated that the less stable the chemical nickel plating bath is, the faster it will initiate the nickel plating of the previously prepared .or activated surface of The results of these tests are illustrated by the curve l0 in Fig. 1; and it will be observed that the amount of nickel reduced chemically at random (as opposed to catalytic plating) is largest at the lower Ni++/ (HZPOQ) ratios, while initiation time and coverage are best with these lower ratios.

Considering another chemical nickel plating bath of the general character of that disclosed in the previously mentioned application of Gutzeit and Krieg, when alkaline earth compounds are used as reagents, the buifer being `a salt of a short chain aliphatic monocarboxylic acid, such as calcium acetate, the optimum concentration of the hypophosphite ions derived from alkali earth hypophosphites is again between 0.15 and 0.35 mole/liter. The initiation time is much shorter, although it is still a function of the NiH/(I-IzPOzV ratio. The following tabulation summarizes tests run in 50 cc. of chemical nickel plating bath at a V/A ratiol of 2.5 on activated general purpose Bakelite samples; the absovthe non-conductive and non-catalytic material. lute concentration of hypophosphite ions derived from calcium hypophosphite was 0.224 mole/'- liter; the buffer was calcium acetate and its concentration in acetate ions was 0.112 mole/ liter; and the initial pH was adjusted to 4.85. In these tests, the nickel plating was carried on for 180 minutes after initiation; and the results were as follows:

Table II Inma' Pntin NiH/(HQPOZV Initial tion time g Sample .Appear- Black precipitate ratio pH time, hrs ance at completion min.

4.86 3 No good (crust)- Considerable. 4.86 2 3 Very good Do. 4.85 4 3 Goodto Fain... Trace. 4.83 5 3 D0. 4. 84 5% 3 D0. 4.71 l5 3 Small amounts.

When using alkaline earth salts both as a aqueous solution of a nickel salt and a hypobuifer and as a source of hypophosphite ions, it is possible to obtain good nickel plating and small amounts of black precipitate by selecting the optimum ratio of Nftit/(HzPOzV at the proper initial pH. The results of these tests are illustrated by the curve 20 in Fig. 2; and it will be observed that the plating results Were excellent at a nickel ion to hypophosphite ion ratio of 0.433, with an initiation time of only 5 minutes, and that only a mere trace of black precipitate was formed during the nickel plating operation. In referring to alkaline earths, we include magnesium.

Finally, considering a chemical nickel plating bath of the general character of that disclosed in the said application of Gutzeit and Ramirez, the bath containing an exaltant in the form of a salt of a short chain aliphatic dicarboxylic acid, such as sodium succinate, the bath is extremely stable, and will initiate nickel plating upon an activated or prepared non-conductive and noncatalytic material only after a long period of time. The following tabulation suinmarizes tests run in 50 cc. of chemical nickel plating bath at a V/A ratio of 2.5 on activated general purpose Bakelite samples; the absolute concentration of hypophosphite ions was 0.225 mole/liter; the exaltant was sodium succinate and its concentration in succinate ions was 0.06 mole/liter; the ratio of Ni++/(H2PO2) was 0.4; and the tests were continued for 60 minutes after initiation of plating occurred. The results were as follows:

In order to obtain faster initiation of the plating process and better coverage by the nickel plating at low pH values with a bath of the character of that disclosed in the said application cf Gutzeit and Ramirez, a slight modication is suggested. This consists in the use of a lower Ni++/ (HzPO2)" ratio in the bath, in the range 0.25 to 0.3.

Recapitulating, in accordance with the process of the present invention, an intimately bondphosphite during a sufcient time interval to cause initial nickel plating upon the growth nuclei and subsequent growth of the nickel plating in a continuous nickel layer upon the fresh non-polarized surface of the body.

From the foregoing, it is apparent that a process has been provided for the plating with nickel of nonconductive and noncatalytic material, such as plastics, hard rubber, wood, ceramics, etc., that involves the preliminary activation or preparation of the surface of the material employing the lpresent method so as to provide thereon rmly anchored growth nuclei minute carbon particles and non-polarized areas accommodating the initiation of the flash nickel coating on the material. Moreover, in carrying out the process of the present invention after activation or prepar-ation of the surface of the material in accordance with the method of the Ipresent invention, an intimately bonded and uniform layer of nickel may be obtained upon the surface of the material -having any desired thickness.

In carrying out the process of the present invention, the carbon employed may take a Wide variety of forms, such as, graphite, lamp-black, channel-carbon, etc.; and the carbon employed may be in powdered, granulated, etc., form, as

' long as it is finely divided.

While there has been described what is at present considered to be the preferred embodiment of the invention, it Iwill be understood that various modifications may .be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. The process of producing an intimately bonded and continuous layer of nickel upon vthe surface of a solid non-metallic body, which comprises ex-posing a fresh non-polarized surface of said lbody having incorporated therein and exposed thereon dispersed growth nuclei minute carbon particles, and immersing said body in a bath consisting essentially of an aqueous solution of a. nickel salt and a hypophosphite during a sufficient time interval to cause initial nickel plating upon said growth nuclei and subsequent growth of the nickel .plating into a continuous nickel layer upon the fresh non-polarized surface of :said body.

2. The process of producing an intimately bonded `and continuous layer of nickel upon the surface of a solid non-metallic body, which comprises exposing a fresh non-polarized surface of said body, securing to the fresh non-polarized surface of said body dispersed growth nuclei minute carbon particles, and immersing said body in a bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite during a sufficient time interval to cause initial nickel plating upon said growth nuclei and subsequent growth of the nickel 'plating into a continuous nickel layer upon the fresh non-polarized surface of said body.

3. The process of producing an intimately bonded and continuous layer of nickel upon the surface of a solid non-metallic body, which comprises abrading the surface of said body to eX- pose a fresh non-polarized surface thereon, securing to the fresh non-polarized surface of said body dispersed growth nuclei minute carbon particles, and immersing said body in a bath consisting essentially of an aqueous solution of a nickel salt Iand a hypophosphite during a sufficient time interval to cause initial nickel plating upon said growth nuclei and subsequent growth of the nickel plating into a continuous nickel layer upon the fresh non-polarized surface of said body.

4. The process of producing an intimately bonded `and continuous layer of nickel upon the surface of a solid non-metallic body, which comprises abrading `the surface of said body with an abrasive material having dispersed therein minute carbon particles so as both to expose a fresh non-polarized surface of said body Iand :to embed in dispersed relation therein said minute carbon particles as growth nuclei, and immersing said body in a bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite during a sufficient time interval to cause initial nickel plating upon said growth nuclei and subsequent growth of the nickel plating into a continuous nickel layer upon the fresh non-polarized surface of said body.

5. The process of producing a composite solid body of non-metallic material having an intimately bonded and continuo-us layer of nickel upon the surface thereof, which comprises compounding Iwith said non-metallic material minute carbon particles, fabricating said body of said compounded non-metallic material and said carbon particles, Iexposing a frh non-polarized surface of said body so that said carbon particles are dispersed as growth nuclei minute particles at the fresh non-polarized surface thereof, and immersing said body in a bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite during a ysufficient time interval to cause initial nickel plating upon said growth nuclei and subsequent growth of the nickel plating into a continuous nickel layer upon the fresh non-polarized surface of said body.

6. The process of producing a composite solid body of synthetic plastic -material having an intimately bonded and continuous layer of nickel upon the surface thereof, which comprises compounding with said synthetic plastic lmaterial carbon particles, fabricating said body of said compounded synthetic plastic material and carbon particles, exposing a fresh non-polarized surface of said body so that said carbon particles are dispersed as growth nuclei minute particles at the fresh non-polarized surface thereof, and immersing said body in a bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite during a suicient time interval to cause initial nickel Iplating upon said growth nuclei and 'subsequent growth of t-he nickel plating into a continuous nickel layer upon the fresh non-polarized surface of said body.

No references cited. 

1. THE PROCESS OF PRODUCING AN INTIMATELY BONDED AND CONTINUOUS LAYER OF NICKEL UPON THE SURFACE OF A SOLID NON-METALLIC BODY, WHIH COMPRISES EXPOSING A FRESH NON-POLARIZED SURFACE OF SAID BODY HAVING INCORPORATED THEREIN AND EXPOSED THEREON DISPERSED GROWTH NUCLEI MINUTE CARBON PARTICLES, AND IMMERSING SAID BODY IN A BATH CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF A NICKEL SALT AND A HYPOPHOSPHITE DURING A SUFFICIENT TIME INTERVAL TO CAUSE INITIAL NICKEL PLATING UPON SAID GROWTH NUCLEI AND SUBSEQUENT GROWTH OF THE NICKEL PLATING INTO A CONTINUOUS NICKEL LAYER UPON THE FRESH NON-POLARIZED SURFACE OF SAID BODY. 